Use the following command to invoke the HAM application:
/usr/lib/hadoop/monitor/ham.sh -conf hadoop-site.xml
This displays a GUI that lists the current values and state of the NameNode and Job Tracker.
You can use this GUI to trigger blocking and non-blocking HDFS operations.
Blocking operations will block until the NameNode has failed over. The blocking operations use the dfs.retry properties. Non-blocking operations will fail if the NameNode is down, but these operations start succeeding once the failover NameNode is live.
